This invention relates to an improved process for making N-alkylpyrrolidones from maleic or succinic derivatives and, more particularly, to processes which reduce maleic derivative using hydrogen to a succinic derivative, or begin with succinic derivative, which derivative is ammonolyzed-alkylated using ammonia and an alcohol to form a N-alkylsuccinimide which is then reduced with hydrogen to form the corresponding N-alkylpyrrolidone.
N-alkylpyrrolidones, in particular N-methylpyrrolidone, are liquid at reasonably low temperatures and because of their powerful dissolving properties have been employed in numerous applications as an extraction and purification solvent. N-methylpyrrolidone has been used in such processes as acetylene recovery from natural gas, butadiene recovery, the separation of aromatics from nonaromatics, sulfur removal from refinery gases, and the dehydration of gas streams. It also has found application as a polymer solvent, being used in the manufacture of resins, fibers, industrial finishes, and in household specialties to overcome incompatibility and improve product performance. Possessing no active hydrogen, it is classified as an aprotic solvent and finds use as a reaction medium in polymer syntheses, for example, alkylated acetylene preparation etc.
Commercially, N-methylpyrrolidone is produced by reacting acetylene with formaldehyde in the presence of a copper acetylide catalyst to generate butynediol. The latter is then hydrogenated to butanediol which is catalytically cyclodehydrogenated to yield 4-butyrolactone. In a final step the butyrolactone is reacted with methylamine to form N-methylpyrrolidone. This technology has several disadvantages. Methylamine and acetylene are both expensive starting materials and the latter presents handling problems as does the formaldehyde. In addition, yields in the four-step commercial process are less than desirable.
Now it has been found that an improved route to N-alkylpyrrolidones starting with a maleic or succinic derivative is available which offers a substantial improvement in process economics because of reduced starting material and processing costs. The improved process is based in part upon the ammonolysis-alkylation reaction of succinic derivatives with ammonia and an alcohol to form N-alkylated compounds.
The thermal reaction with primary amines to form N-alkylpyrrolidones is well documented in the patent literature. See, for example, U.S. Pat. No. 2,643,257, Ger. Offen. No. 2,164,350 and Brit. Pat. No. 1,367,629. In addition, the alkylation of amides and imides via an alcohol is also described. See J Am Chem. Soc 94 679 (1972) and 87, 5261 (1965). For example, phthalimide alkylation to the N-alkylimide has been accomplished in two steps by first making the potassium salt of phthalimide and subsequently reacting it with an alcohol. The use of a combination of ammonia and hydrogen to convert a diethylmaleate/ethanol solution catalytically to 2-pyrrolidone is described by Japanese authors in Y. Kogyo Kagaku Zasshi 73,545 (1970). The catalyst was a nickel or cobalt material. Pyrrolidones have been alkylated catalytically via alcohols to N-alkylpyrrolidones by Japanese workers. See, for example, Japanese Kokai No. 76-16,657. Reduction using hydrogen of succinimide and N-methylsuccinimide to pyrrolidone and the N-methyl derivative has also been extensively reported. See, for example, U.S. Pat. Nos. 3,092,639, 3,745,164 and 3,681,387. Equally, hydrogenation of maleic anhydride and its derivative to pyrrolidone and N-alkylpyrrolidones using ammonia and hydrogen is taught in U.S. Pat. Nos. 3,808,240, 3,198,808 and 3,080,377.